Field of the Invention
The present invention relates to a developing apparatus having a developer bearing member that bears developer and rotates, and to an image forming apparatus, such as a copying machine, a printer, a facsimile, or a multifunction machine equipped with these functions, having the developing apparatus.
Description of the Related Art
Image forming apparatuses adopting an electrophotographic system or an electrostatic recording system include a developing apparatus that develops an electrostatic latent image formed on a photosensitive drum serving as an image bearing member using toner and other developer. The developing apparatus includes a developing sleeve serving as a developer bearing member that bears developer and rotates, and the developer borne on the developing sleeve is supplied to the photosensitive drum.
Some developing apparatuses use a two-component developer that includes nonmagnetic toner particles, i.e., toner, and magnetic carrier particles, i.e., carrier, as developer. Especially, in color image forming apparatuses, two-component developer is generally used due to reasons such as good color quality, since there is no need to mix magnetic substance to toner. Recently, longer life has been realized in the developing apparatuses that use two-component developer, and the developing apparatus is only replaced two to three times during the life of the image forming apparatus body. Along therewith, the life of developer contained in the developing apparatus is also elongated, and a state where developer in a certain deteriorated state is used continuously is continued for a long time.
Therefore, charge imparting property of carrier to replenished toner is also deteriorated compared to the initial state, and a state where distribution of amount of charge of developer is relatively low continues for a long time. In this state, the toner having a low amount of charge has deteriorated electrostatic adhesion force with carrier particles and may easily be separated, such that probability of toner scattering in air caused by agitation or conveyance action of toner in the developing apparatus, or by formation of magnetic bristles, is increased. Thus, toner may be scattered to the exterior of the developing apparatus and adhere to the optical path of a laser scanner and interfere with formation of latent image, causing image defects such as generation of white lines on the image.
Hitherto, for example, as disclosed in Japanese Patent Laid-Open No. 2014-178347, a technique of suppressing scattering of toner within an apparatus has been developed. In this Japanese Patent Laid-Open No. 2014-178347, a configuration is disclosed in which a filter is used to reduce internal pressure of the developing apparatus, thereby preventing toner from scattering through a gap formed between a developer container and a developing sleeve, for example.
However, according to the configuration disclosed in Japanese Patent Laid-Open No. 2014-178347, a filter is used to reduce toner scattering, such that the apparatus cannot correspond to short-term pressure fluctuation due to pressure loss generated at the filter, and the pressure is stabilized slowly. If a rough filter that generates small pressure loss is used as the filter that corresponds to a short-term pressure fluctuation, scattered tonner cannot be collected sufficiently, and the scattered toner may leak to the exterior of the developing apparatus.
One of the problems of toner scattering is that it is sometimes caused by replenishment of toner, in addition to the normal developer agitation. The scattering of replenished toner is not a phenomenon that occurs constantly, and it occurs only at a timing of replenishment operation, but the amount of scattering of toner is great, such that there is a need to perform airflow control when this phenomenon occurs. Specifically, replenished toner discharged from a container storing replenished developer reaches a replenishing portion of the developing apparatus. During this process, replenished toner scatters when falling in the air, and shock generated when the toner falls to a developer surface of developer in the developing apparatus causes toner to fly up and scatter. Further, toner may scatter in the air when toner or developer containing a high ratio of toner is agitated by an agitating screw provided in the developing apparatus.
However, according to the configuration disclosed in Japanese Patent Laid-Open No. 2014-178347, toner scattering is reduced by stabilizing pressure using a filter, such that if a large amount of toner scattering occurs only when toner is replenished, it is not possible to collect scattered toner sufficiently, and the scattered toner may leak to the exterior of the developing apparatus.